In manufacturing a semiconductor integrated circuit, there is a process of forming a titanium nitride (TiN) film as a metal barrier layer, or forming a titanium silicide (TiSix) film as an intermediate protection layer underlying the TiN film. The TiN film and the TiSix film are formed by heating a titanium (Ti) film formed on a semiconductor wafer (hereinafter, referred simply to as a “wafer”) inside, e.g., a vertical heating furnace of a heat treating apparatus and simultaneously, exposing the same to ammonia (NH3) and disilane (Si2H6).
The wafer on which the TiN film is formed, is stored and transferred in an atmosphere of a sufficiently reduced oxygen concentration using an internally-sealed wafer carrier such as a Front Opening Unified Pod (FOUP). With this configuration, the wafer can be transferred up to a heating unit without oxidizing the Ti film.
However, in a loading region defined below the heating furnace inside the heating unit, the wafer is exposed to an atmospheric atmosphere, which oxidizes the TiN film. This increases a resistivity of the TiN film or the TiSix film, which is formed by exposing the Ti film to the NH3 gas or the Si2H6 gas.
For this reason, an inert gas is supplied to the loading region to form an atmosphere of a reduced oxygen concentration and to prevent the surface of the Ti film from being oxidized. Specifically, sealability of a box structure having a box shape which constitutes the loading region is increased, and the inert gas is supplied to keep an internal space of the box structure in a positive pressure. This prevents the outside air from being introduced into the internal space of the box structure. In addition, the internal space is purged by the supplied inert gas so that the oxygen concentration in the internal space is reduced.
In order to efficiently prevent the oxidization of the surface of the Ti film, there is a need to supply a mass of inert gases to the box structure so as to reduce the oxygen concentration in the loading region as much as possible. Unfortunately, the supply of the mass of the inert gas increases manufacturing costs of an integrated circuit (IC). To overcome this problem, there is a need to further increase the sealability of the box structure to thereby reduce the supply amount of the inert gas.
However, in a case where the internal space of the box structure is kept in the positive pressure by the inert gas, it has proved that, although few outside air is directly introduced into the internal space of the box structure, when a small amount of the inert gas is leaked from the box structure to the outside, the outside air is reversely diffused to the internal space. This makes it difficult to realize a reduced oxygen concentration, e.g., 10 ppm or less, which is required to prevent the oxidization of the Ti film, in the internal space of the box structure.